The purpose of this study is to delineate the effect of exogenously induced changes in the lipid composition of membranes on the activity of membrane-bound enzymes, transport, and biosynthetic adaptability. The cell type used will be anaerobically grown yeast, since it is experimentally possible to prevent endogenous biosynthesis of sterol and fatty acid by exclusion of oxygen. The results will further elucidate the basic phenomena governing and resulting from the architectural roles of sterols and phospholipids in organelles and will provide a basis for understanding disease states in which the lipid composition of membranes is abnormal.